In many industries, such as paper making, food processing, and textiles, or any other industry that processes a web of material, rolls are used for various types of processing functions, and in many instances, the straightness of the roll is very important. For example, in a paper making assembly, roll deflection may adversely affect the quality of the product being produced because the surface of the paper reflects the shape of the roll over which it passes. Thus, it is desirable for the rolls to be as smooth as possible and devoid of any imperfections, deflections or variations so that the paper that is formed will be smooth and uniform. In addition to resulting in the production of inferior products, roll deflection may also result in damage to the roll itself or the machinery containing the roll. Thus, various attempts have been made to control the shape of rolls so as to avoid the problems described above.
U.S. Pat. No. 5,785,636 to Bonander discloses a roll having an outer surface made of a fabricated fiber matrix for strengthening and reinforcing the roll to minimize roll deflection.
U.S. Pat. No. 2,908,964 discloses a controllable convex roll having a pressure fluid chamber positioned between a roll axle and the roll shell. Adjusting the pressure in the pressure fluid chamber controls deflection of the roll shell. However, the roll disclosed in the '964 patent has a number of problems associated therewith including sealing difficulties resulting in leakage of pressure fluid. In addition, the roll disclosed in the '964 patent has a relatively slow response time for changing the pressure of the pressure fluid, requiring about 30 seconds to increase the pressure and about 10 seconds to decrease the pressure. As a result, the '964 patent system is unable to rapidly respond to deflections in the roll and a considerable quantity of paper is wasted when such a roll is used in paper machines. Moreover, rolls having a convex exterior surface have a limited operating range and may obtain a uniform pressure across the exterior surface only at a given load.
U.S. Pat. No. 5,197,174 to Lehmann discloses a controlled deflection roll having a rotatable roll shell supported by a row of hydraulic support elements. The support elements are connected with fluid lines that supply hydraulic fluid to the support elements for generating a pressure force at the exterior surface of the roll. The '174 patent also discloses a control device which controls the supply of the hydraulic fluid sent to each hydraulic support element. However, the Lehmann system also has a relatively slow response time for correcting a roll deflection condition.
U.S. Pat. No. 4,301,582 to Riihinen discloses a system that removes deflections from a roll using magnetic forces. The roll has a non-rotating axle with ends having a load imposed thereat and a cylindrical shell rotatably supported by bearings on the axle. A magnetic core is formed in the axle and a plurality of pole shoes are spaced from the shell by an air gap. A plurality of electromagnetic windings, each wound on the core at one of the pole shoes, produce a magnetic compensating force field between the shell and the core for responding to deflections in the roll.
U.S. Pat. No. 4,357,743 to Hefter, et al., discloses a controlled deflection roll having a roll shell which is radially movable in at least one plane in relation to a roll support. Position feelers or sensors are arranged at the ends of the roll shell for detecting one or more deflections in the roll shell as a function of deviations from a predetermined reference or set point. The position feelers control regulators operatively associated with pressure or support elements positioned between the roll support and the roll shell so that the roll shell is maintained in the reference or set position.
U.S. Pat. No. 4,062,097 to Riinhinen discloses a roll having magnetic deflection compensation that may be used in the calender or press section of a paper machine. The roll has an inner non-rotating axle and an outer shell surrounding and rotatable with respect to the axle, the axle and the shell having a common axis. The axle includes an inner magnetic structure while the shell includes an outer magnetic structure that rotates together with the shell. These inner and outer magnetic structures cooperate to provide attraction between the shell and axle on one side of the above axis and repulsion between the shell and axle on the opposite side of the axis, thereby achieving deflection control and/or compensation.
Other techniques used to reduce the detrimental effects of roll deflections include running process machinery at slower speeds in order to avoid resonance problems, and using back-up roll systems to reduce deflections. Further techniques include floating a roll in a fluid medium or using plural bearings for each bearing journal.
Therefore, there is a need to have a deflection control system for a roll that rapidly eliminates deflections in a roll. There is also a need for a deflection control system that effectively responds to deformations of the roll caused by various sources such as induced vibrations, external loading and thermal loading. There is also a need for a deflection control system that enables deflections to be induced into the roll for any purpose necessary.